108 AGBICULTUBE. fc 



being diminished in proportion to the water which runs off. 

 Into the spot which offers no resistance, be it large or be 

 it small, the water above that level must be pushed till the 

 column is so reduced that its weight will not overcome 

 friction. As friction will be greatest at the intermediate 

 point between two parallel drains, the water will stand a 

 little highest at that point and will decline in a regular 

 gradation to the level of the bottom of each drain. Take 

 a familiar illustration for, like Walter Blith, we are 

 obliged to use repetitions, though we will not follow his 

 example in saying why. In a soil which is saturated with 

 water (and by saturated we mean that, in addition to its 

 water of attraction, it has the interstices between its par- 

 ticles filled with water of drainage) sink a deep hole, no 

 matter how narrow ; it will stand full of water. Draw the 

 water out rapidly it will fill again from the bottom. Into 

 the space where there is no resistance the water must come. 

 This is a parallel case to the bottom of the drain from 

 which the water runs off the point of non-resistance re- 

 mains, and to it all the water in the soil must come up to 

 the limit which we have above assigned. Will the small 

 pipes carry off the water? This is a mere question of 

 capacity, and can be decided by accurate calculation ; the 

 calculation is given at length in pp. 43-45 of Mr. Parkes's 

 Essays. We will only state the result. If an acre of land 

 be intersected with parallel drains 12 yards apart, and if 

 on that acre should fall the very unusual quantity of 

 1 inch of rain in 13 hours, in order that every drop of 

 this rain may be discharged by the drains in forty-eight 

 hours from the commencement of the rain (and in a less 

 period that quantity neither will, not is it desirable that it 

 should, filter through an agricultural soil) the interval 

 between two pipes will be called upon to pass two-thirds of 

 a table-spoonful of water per minute, and no more. Inch 

 pipes, lying at a small inclination, and running only half- 

 full, will discharge more than double this quantity of water 

 in forty-eight hours. The mains or receiving drains are of 



